Neural communication among rhombencephalic auditory structures is being explored by means of single-unit recordings in the decerebrate, unanesthetized cat. The response characterisitcs of central nervous system axons that are efferent from and afferent to the cochlear nuclei are examined. Both extracellular and intracellular recordings are made. A few fibers are injected with horseradish peroxidase after physiological characterization and their somatic origin and terminal distributions determined. Fiber response characteristics are compared with single unit responses previously recorded in our laboratory from the cochlear nuclei and superior olivary complex. The studies examine neuronal circuits involved in the formation of receptive field features of the principal cells of the dorsal cochlear nucleus, octopus cells of the posteroventral cochlear nucleus, and neurons of the superior oblivary complex. The experiments test for the possibility that axonal response characteristics differ from those recorded somatically. The neural substrates, spike train coding and synaptic mechanisms by which information is abstracted in the central auditory system (including mechanisms for binaural interactions) may be revealed.